Uranium can be recovered from commercial grade wet process phosphoric acid by an oxidative extraction-reductive stripping process. In this process, an oxidized phosphoric acid solution is contacted, generally in a multistage, counter-current extractor, with an organic extractant solvent composition having an affinity for oxidized uranium values. After extraction, two phases are formed, namely an oxidized, aqueous acid raffinate phase and an organic solvent phase rich in oxidized uranium values. Then, the organic solvent phase is reductively stripped of its uranium content, by a strip acid solution, generally in a multistage countercurrent reductive stripper. The stripped, barren organic solvent, containing reducing materials, is then generally passed to a decanter, to allow entrained strip acid to settle, and returned to the extraction system.
The uranium can be recovered from the strip acid by first again oxidizing the acid and then re-extracting the oxidized uranium in a second cycle extraction. The uranium can be recovered from the second cycle solvent using an ammonium carbonate strip solution and a precipitation stage. This process is well known in the art, and is taught for example by Hurst et al., in U.S. Pat. No. 3,711,591; Elikan et al., in U.S. Pat. No. 3,966,873 and Sundar, in U.S. Pat. No. 4,002,716.
Decanting the barren, organic solvent after the first cycle stripping, allows entrained strip acid to separate from the barren solvent to a certain extent, before the solvent is recycled to the extractor. However, humic acid gunk and other solids accumulate in the decanter. The barren, organic solvent also evidences a lowering of extraction efficiency when it is recycled to the extractor, because the entrained acid reduces the uranium in the extraction acid. Smith et al., in U.S. Pat. No. 4,190,633, recognized acid entrainment and solids accumulation problems in the uranium rich organic solvent phase; and attempted to solve them, before the stripping stage, by clarification, water wash, and caustic treatment with NaOH and Na.sub.2 C0.sub.3, to produce regenerated organic solvent. This process, however, involves five separate steps, use of caustic chemicals, and would not solve extraction efficiency problems.